Millions of Americans order hamburgers, pizza, fried chicken, coffee or some other item every day from one of almost 300,000 fast-food restaurants across the country. But some fast-food chains are losing customers and closing stores as consumers flock to fast-casual restaurants that emphasize distinctive, creatively prepared food and eco-friendly production. To compete, major fast-food companies have begun offering healthier menu items in addition to the high-calorie options that remain popular with many consumers. Some restaurants also are working to reduce pollution linked to their operations. And certain chains, including White Castle, serve plant-based, meatless burgers designed to appeal to health-conscious and environmentally minded consumers. In the race to stay relevant with teens and young adults, McDonald's and other chains are relying increasingly on mobile delivery apps and buzz-worthy internet promotions. Rising labor costs, meanwhile, have led to higher prices for some fast-food items, and to predictions that the industry will rely more on robots and less on human workers in the future.

An Impossible Slider, which consists of plant protein but is made to taste like a beef hamburger, sits on a table at a White Castle restaurant in New York City. Fast-food chains are increasingly modifying their menus to try to meet consumer demand for healthier food that reflects a concern for the environment. (Getty Images/Drew Angerer)